1) Field of the Disclosure
The disclosure relates generally to composite structures and methods, and more specifically, to laminated composite radius fillers for composite structures, such as structures for aircraft, and methods of forming the same.
2) Description of Related Art
Composite structures, such as structures made of carbon fiber-reinforced plastic (CFRP) materials, may be used in a wide variety of applications, including in the manufacture of aircraft, spacecraft, rotorcraft, watercraft, automobiles, trucks, and other vehicles and structures, due to their high strength-to-weight ratios, corrosion resistance and other favorable properties. In particular, in aircraft construction, composite structures may be used to form the tail sections, wings, fuselage and other components.
When composite structural members are joined together, such as reinforcing stiffeners or stringers joined to composite skin panels, gaps or voids regions, typically referred to as “radius filler regions” or “noodle regions”, may be present along bond lines between the composite structural members. Radius filler elements or “noodles” made of composite material or adhesive/epoxy material and having a generally triangular cross-section may be used to fill the radius filler regions or noodle regions in order to provide additional structural reinforcement to such regions.
The radius filler element or noodle used to fill the radius filler region or noodle region may be in the form of a laminated composite radius filler. Such known laminated composite radius fillers may be made of laminates formed of stacked composite plies. However, during manufacturing cure and thermal cycling stages of such known laminated composite radius fillers, such as used in composite structures including reinforcing stiffeners or stringers, delamination or layer separation may occur in the laminated composite radius fillers. Generally, such delamination occurs in an upper one-third area near the tip of the laminated composite radius filler and may occur more frequently in larger laminated composite radius fillers. Such delamination is typically caused by a difference in the coefficient of thermal expansion (CTE) between the plies adjacent to the laminated composite radius filler, i.e., wrap plies, and the laminated composite radius filler.
Known solutions to address such delamination of the laminated composite radius filler exist. For example, one such known solution involves showing that the delamination of the laminated composite radius filler is not detrimental. However, such known solution may add risk since it may be difficult to show that the delamination will not grow to a detrimental size under all environmental and loading conditions throughout the life of a composite structure.
Thus, it is desirable to be able to solve the issue of delamination of laminated composite radius fillers used in composite structures, such as reinforcing stiffeners and stringers. Accordingly, there is a need in the art for improved laminated composite radius fillers and methods of forming the same that provide advantages over known elements, assemblies and methods.